Experimentally optimized particle–polymer matrix structure for efficient daytime radiative cooling

The polymer–particle matrix structure has attracted great interest for daytime radiative cooling due to its various advantages; however, cost-effective fabrication process development and proper material selection are crucial tasks. Herein, we illustrate the selection of fabrication process and materials based on development, characterization, and experimental performance. The initial selection is based on solar radiation backscattering and isotropic thermal emission properties of polymers and particles. Among potential polymers (PMMA, PVDF, and PU), PMMA is experimentally found more suitable for radiative cooling because of negligible absorption in the solar radiation spectrum. Among the selected particles (CaCO3, BaSO4, ZnO, and SiO2), the experimental performance of BaSO4 in the polymer matrix is found to be excellent. Furthermore, the optimum particle volumetric concentration is found at 70%, with an optimum thickness of 500 μm for the substrate independent radiative cooler. Spray-coating is found to be a better option for fabrication as compared to drop casting. The performance evaluation was carried out at Varanasi, India for over two months to investigate the environmental parameters' effect on performance. For an optimized structure, the observed maximum temperature drop from the ambient is 6 °C (17 °C lower than bare roof surface) during noontime and 9 °C during the evening. At ambient temperature, the recorded cooling power is 35 W/m2 at noon (solar peak) and 78 W/m2 in the evening for the experimentally optimized structure.